A sequel would basically write itself with all that Star Trek reboot and Star Wars sequel stuff going on.

Producers want to reboot Galaxy Quest, spouting stuff like how lame the original was, how pathetic the fans are, etc... the original cast is outraged that they are going to be replaced by a bunch of tweenagers. Especially Tim Allen, because he is not getting asked for a cameo, but Alan Rickman ist. But then they and the reboot cast are sucked into another interstellar adventure aboard the Protector. With time travel and alternate universes, so that they actually do reboot reality.